The present invention relates to an in-cylinder injection type spark ignition internal combustion engine installed in a motor vehicle, and in particular to a SOHC type in-cylinder injection gasoline engine.
In the field of spark ignition type internal combustion engines installed in motor vehicles, various types of in-cylinder or direct injection type gasoline engines have been proposed in recent years, wherein a fuel is directly injected into a combustion chamber, instead of an intake pipe as in conventional engines, in an attempt to reduce harmful components of exhaust gases, and improve fuel economy. One example of such in-cylinder injection type gasoline engines is disclosed in U.S. Pat. No. 5,305,720 (Japanese Laid-open Patent Publication (Kokai) No. 5-240044).
In the in-cylinder injection gasoline engine disclosed in the above-identified publication, each intake port is formed as an upright port that extends substantially straight in a vertical direction, so that the air is sucked into a combustion chamber with a high intake or suction efficiency, so as to produce a swirl (reverse tumble flow) in the vertical direction within the combustion chamber. A cavity is formed in the top face of the piston. In operation, the fuel is injected from a fuel injector toward the cavity, for example, during a compression stroke, so that an air-fuel mixture whose air-fuel ratio is close to the stoichiometric ratio can be formed around a spark plug at an ignition timing, due to the swirl flowing across the bottom face of the cavity, even where the amount of the injected fuel is small.
Accordingly, the in-cylinder injection gasoline engine of the above type is able to successfully fire or ignite an air-fuel mixture even if it has a large air-fuel ratio as a whole, namely, the combustion chamber as a whole contains a fuel-lean air-fuel mixture, thus showing a high combustion efficiency. Further, the amount of discharge of harmful components of exhaust gases, such as carbon monoxide (CO) and hydrocarbon (HC), can be reduced, and the fuel economy can be improved mainly during idling of the engine or running of the vehicle with a low load.
The in-cylinder injection gasoline engine disclosed in the above-identified publication is provided by constructing a DOHC (double over head camshaft) type gasoline engine so that the fuel can be directly injected into the combustion chamber or cylinder.
However, the DOHC type gasoline engine is provided with two camshafts, and therefore suffers from a problem of relatively high manufacturing cost. The use of the two camshafts also results in an increase in the dimension of a cylinder head as measured in the width direction, which eventually results in an increase in the size of an engine body. If the size of the engine body is thus increased, the size of the engine as a whole cannot be reduced even if the in-cylinder injection gasoline engine has a relatively small displacement, thus making it difficult to install the engine on the vehicle.
In view of the above problem, it may be considered to construct an in-cylinder injection gasoline engine based on a SOHC (single over head camshaft) type gasoline engine that may have a reduced size and is available at a relatively low manufacturing cost, by providing the SOHC type engine with a fuel injection valve (injector) that is able to inject the fuel into the combustion chamber formed in the cylinder.
In this case, intake and exhaust ports, spark plug and other components of the SOHC type in-cylinder injection gasoline engine need to be located at appropriate positions relative to the single camshaft, so that the in-cylinder injection gasoline engine exhibits a high combustion efficiency that is equivalent to that of the DOHC type in-cylinder injection gasoline engine as described above.
It is therefore an object of the present invention to provide an in-cylinder injection type spark ignition internal combustion engine whose constituent components are located at appropriate positions when the engine is of a SOHC type, and which exhibits a high intake efficiency and combustion efficiency, and can be produced in reduced size.
To accomplish the above object, the present invention provides a four-valve type internal combustion engine of a SOHC type having a single camshaft, which is provided with a fuel injector capable of injecting a fuel directly into a combustion engine. Thus, even in the SOHC type internal combustion engine, the fuel is injected into each cylinder during a compression stroke, to be directed towards a spark plug, so that a fuel spray is concentrated at around the spark plug, to achieve stratified charge combustion in a desirable manner. This enables the engine to operate with a fuel-lean air-fuel mixture having a considerably large air-fuel ratio, thus assuring improved combustion efficiency and improved fuel economy.
In the SOHC type internal combustion engine according to the present invention, the intake port communicates at one end thereof with two openings that open to the combustion chamber, and at least a part of the intake port extends toward an upper surface of the cylinder head, so as to pass through a region between the shortest lines that connect distal ends of respective shaft portions of two valve members of one of the intake valve and exhaust valve, with the camshaft, as viewed in a direction of the axis of the cylinder. Namely, the intake port is disposed so as to extend between one of the intake valve and exhaust valve and the camshaft. Accordingly, the space in the cylinder head can be efficiently utilized, and a dimension of the internal combustion engine, as measured in its width direction, can be reduced, which leads to reduction in the size of the internal combustion engine. Further, the intake air can be introduced into the combustion chamber with a high suction efficiency, to flow in the vertical direction along the side wall of the cylinder, so that a swirl (reverse tumble flow) which rotates in the vertical direction can be favorably produced in the combustion chamber, thus assuring a further improved combustion efficiency. Thus, the four-valve type internal combustion engine of the SOHC type of the present invention is able to yield substantially the same effects as provided by known DOHC type in-cylinder injection gasoline engines.
In this connection, the intake port is preferably formed as an upright port that extends substantially in parallel with the axis of the cylinder. In this case, the dimension of the internal combustion engine, as measured in the width direction, can be further reduced, with a result of further reduction in the size of the internal combustion engine. Also, the intake air can be inducted into the combustion chamber with a further improved intake or suction efficiency, to flow in the vertical direction along the side wall of the cylinder, whereby the combustion efficiency of the engine can be further improved.
In one preferred form of the present invention, a spark plug is located to be exposed to a generally central portion of the combustion chamber, and an insertion hole that receives the spark plug extends through the cylinder head on the side opposite to the intake port, namely, extends between the other of the intake valve and exhaust valve and the camshaft. In this arrangement, the insertion hole for the spark plug as well as the intake port can be formed in a desirable fashion so that the spark plug is located at the optimum position, and the thus obtained in-cylinder injection type internal combustion engine exhibits not only an improved suction efficiency but also a significantly improved combustion efficiency, and can be produced in reduced size.
In another preferred form of the invention, the intake port consists of two independent port portions that respectively communicate with two intake openings formed at the lower surface of the cylinder head. In this case, a single rocker arm is rockably supported by a rocker shaft, for driving two valve members of each of the intake and exhaust valves, and therefore the size and weight of the rocker arm can be reduced. Further, the intake port can be favorably disposed between the intake valve and the camshaft, without interfering with the rocker arm.
If the intake port consists of two independent port portions as described above, the location of each port portion and the area of a passage provided by the port portion can be determined with a high degree of freedom. Namely, if two independent port portions are used, the intake port can be easily located at a suitable position and the area of the passage can be easily set so that the optimum intake or suction efficiency can be achieved.
In a further preferred form of the invention, the intake port is provided by a branch pipe that includes an upstream portion which consists of a single port portion, and a downstream portion which consists of two port portions diverging from the upstream, single port portion. The two port portions are directed at the two openings for communication therewith. In this case, a rocker arm which is rockably supported by a rocker shaft for driving two valve members of the intake valve is disposed so as to sandwich the single port portion of the intake port therebetween, as viewed in the direction of the axis of the cylinder. Thus, the intake port is favorably disposed between the intake valve and the camshaft, without interfering with the rocker arm.
If the intake port is constructed as a branch-pipe type port wherein two port portions diverge or bifurcate from a single port portion as described above, the area of a passage provided by the single port portion can be made relatively large, and the amount of intake air can be accordingly increased. Thus, the use of this type of intake port make it easy for the engine to operate with a fuel-lean air-fuel mixture having a large air-fuel ratio, where a large amount of intake air is required.